Circuit board construction for use in small form factor fiber optic communication system transponders

ABSTRACT

A transponder assembly for use with fiber optic digital communication cables having multiple parallel optic fiber elements. The transponder assembly features separate transmitter port and receiver ports and an electrical connector for connecting with computer or communication systems. The transponder assembly includes a parallel optic transmitter module and a parallel optic receiver module. The assembly also includes a circuit board on which a semiconductor chip useful for signal processing and the electrical connector are mounted. A Flex circuit is used in connecting the circuit board to the parallel optic modules. The semiconductor chip and electrical connector are mounted directly across from one another on opposite surfaces of the circuit board using ball grid arrays having overlapping attachment structures.

FIELD OF THE INVENTION

[0001] The present invention relates to the use of optoelectronic components in fiber optic digital communication networks and, more particularly, to transponder assemblies and the electrical and circuit components within them.

BACKGROUND OF THE INVENTION

[0002] The majority of computer and communication networks in use today rely on copper wiring to transmit data between network nodes. However, electrical signals carried by copper wiring have a limited capacity for carrying digital data.

[0003] Many computer and communication networks, including large parts of the Internet, are now being built using fiber optic cabling that can be used to transmit much greater amounts of data. With fiber optic elements data is transmitted using optical signals (sometimes referred to as photonic signals) having greater data carrying capacity.

[0004] However, since computers use electrical signals as opposed to optical signals, the light signals used to transmit data over fiber optic links must be translated to electrical signals and vice-versa during the optical communication process. Building such fiber optic networks therefore requires optoelectronic modules which electrically and optically interface optical transmission mediums such as fiber optic cables with electronic computing and communications devices. Further, in order to provide the required bandwidth for very high-speed communications, fiber optic ribbon cables having multiple fiber optic elements and so-called “parallel optics” modules adapted for transmitting or receiving multiple signals over such may also be used.

[0005] The optoelectronic modules associated with fiber optic networks should therefore be adapted for accommodating fiber optic ribbon cables having multiple fibers. Further, it is desirable for separate parallel optic transmitter and receiver modules to be incorporated in transponder assemblies which can separately transmit and receive optical data over separate cables using the transmitter and receiver modules. However, for most applications these transponder assemblies must be compact and should utilize only the smallest possible footprint on the circuit boards within the electronic computing or communications devices with which the fiber optic network is interfacing. Accordingly, the components and circuitry within the transponder assembly must be designed to have the smallest possible dimensions.

SUMMARY OF THE INVENTION

[0006] The transponder assembly of the present invention comprises a small form factor system for interfacing between computer and communication systems and fiber optic cables having multiple fiber elements while providing concurrent electrical-to-optical and optical-to-electrical conversion functionality. The transponder assembly features a pair of optical communication ports one of which functions as a transmitter port and the other of which functions as a receiver port for interconnecting with parallel optics fiber optic ribbon cables. The transponder assembly also features a circuit board having a pin-array electrical connector and a semiconductor chip adapted for signal processing such as a SerDes chip mounted on different surfaces of the board.

[0007] The transponder assembly includes a parallel optics transmitter module and a parallel optics receiver module having pluggable edge connectors. A flexible printed circuit or Flex circuit is used to flexibly connect the circuit board to a connecter board mounting a pair of connection jacks which interconnect with the edge connecters of the parallel optics modules. The semiconductor chip and pin-array connector are mounted directly across from one another on opposite surfaces of the circuit board using ball grid arrays having areas in which their attachment structures overlap. The vias associated with the two ball grid array attachments are positioned in between one another in the overlapping areas. The solder pads associated with the vias having the same connection functionality are interconnected by surface traces and redundant vias are eliminated in order to allow adequate pathways for circuit traces to within the circuit board structure to extend through the overlapping areas of the ball grid array attachments. Placement of the pin-array connector and semiconductor chip across from one another on the circuit board allows for an assembly having minimum lateral dimensions.

[0008] It is an object of the present invention to provide a transponder assembly adapted for use with fiber optic ribbon connectors having multiple fiber optic elements.

[0009] It is another object of the present invention to provide a transponder assembly which utilizes separate parallel optic transmitter and receiver modules in an assembly having a compact size and minimum footprint.

[0010] It is a further object of the present invention to provide for the internal components of a parallel optics transponder assembly to be flexibly interconnected whereby a compact size can be achieved.

[0011] It is yet another object of the present invention to provide for the a semiconductor chip and an electrical connector be positioned directly across from one another on same circuit board using ball grid array attachments on opposite surfaces of the same circuit board to electrically interconnect the semiconductor chip, electrical connector and circuit board.

[0012] It is a yet further object to provide an efficient and effective parallel optics transponder assembly featuring a compact size and small footprint.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention and its advantages may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

[0014]FIG. 1 is an overhead, perspective view of a transponder assembly constructed in accordance with the principles of the present invention primarily showing the communication ports by which the assembly can be optically connected to a pair of fiber optic ribbon cables for separately transmitting and receiving digital data over separate cables.

[0015]FIG. 2 is a perspective view of the underside of the transponder assembly shown in FIG. 1 primarily showing the pin-array connector for electrically the assembly to a circuit board or the like of a computer or communications system.

[0016]FIG. 3 is an overhead, prospective view of the transponder assembly of the present invention with the top section of the assembly housing removed showing the internal components within the transponder assembly and showing, among other things, the parallel optic transmitter and receiver modules within the assembly.

[0017]FIG. 4 is a side view of the internal components of the transponder assembly of the present invention showing, among other things, the parallel optic modules, a connector board with connection jacks, a Flex circuit and a rigid circuit board on which a SerDes chip and pin-array connector are mounted on opposing surfaces of the board.

[0018]FIG. 5 is a close-up side view along lines 5-5 in FIG. 4 of the connecter board, Flex circuit and rigid circuit board components primarily illustrating how these components are flexibly interconnected and aligned.

[0019]FIG. 6 is a close-up cross-sectional view of a typical section of the rigid circuit board on which the SerDes chip and pin-array connector are mounted showing an area in the vicinity of one of the ball grid arrays associated with either the chip or the connector.

[0020]FIG. 7 is an overhead, plan view of the circuit board on which the SerDes chip and pin array connector are mounted showing the ball grid array attachment structures associated with the SerDes chip and the pin array connector.

[0021]FIG. 8 is a close-up cross-sectional view of a typical section of the rigid circuit board on which the SerDes chip and pin-array connector are mounted showing an area of overlap between both of the ball grid arrays associated with the SerDes chip and pin-array connector.

[0022]FIG. 9 is a close-up overhead, plan view of the circuit board on which the SerDes chip and pin array connector are mounted exclusively showing ball grid array attachment structures associated with both the SerDes chip and pin-array connector in one of the overlapping areas between the ball grid arrays and their attachment structures.

[0023]FIG. 10 is an exploded, overhead perspective view of parallel optics module which comprises one of the primary components of the transponder assembly of the present invention showing, among other things, how the receptacle, lens and alignment frame, carrier frame section, circuit board, edge connector and the other components and subcomponents of the module relate to one another.

[0024]FIG. 11 is an enlarged exploded, overhead perspective view of the forward portion of the module shown in FIG. 10 primarily showing, how the receptacle, lens and alignment frame, carrier frame section and their subcomponents relate to one another.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will now be described in detail with reference to preferred embodiments as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it should be apparent to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances it should be appreciated that well-known process steps have not been described in detail in order to not obscure the present invention.

[0026] Referring now to FIGS. 1 and 2, a transponder assembly 10 is shown as including a two-piece housing 12, two communication ports 14 and 16, a pin-array type electrical connector 18 and a heat sink 20. The pin-array connector 18 is preferably a 300-pin MEG-Array™ electrical connector (which may be purchased from FCI USA, AREVA Group, having US offices at 825 Old Trail Road in Etters, Pa., 17319). The two-piece housing 12 includes a top section 22 and a bottom section 24 which are fitted together to form a small form factor case enclosing the operational modules of the transponder assembly 10. The communication ports 14 and 16 reside on its front side of the assembly 10 and include parallel optical link receptacles 26 and 28 which are part of parallel optics modules 30 and 32 (not otherwise shown in FIGS. 1 and 2) deployed within the transponder 10. The receptacles 26 and 28 are designed to mate with standard MTP™ (MPO) connectors (Optical Internetworking Forum, OIF-VSR4-03.0) of fiber optic ribbon cables containing 12 parallel fibers and presenting 12 fiber optic terminations for optical interconnection. The pin-array connector 18 resides on the underside of the transponder assembly 10 and includes a 300-pin plug housing 25 for connecting to a printed circuit board or other electrical assembly having a matching Pin-array receptacle housing. The port 14 is associated with the parallel transmitter module 30 which is adapted for converting electrical signals into optical signals and transmitting these signals into a fiber optic ribbon cable connector. The port 16 is associated with the parallel optics receiver module 32 which is adapted for receiving optical signals from a fiber optic ribbon cable connector and converting the same into electrical signals. The ports 14 and 16 thereby provide transmitter and receiver links so that the transponder 10 can both receive and transmit data over separate 12 fiber element parallel optic ribbon cables. The heat sink 20 includes a set of ribs 35 to allow for improved heat dissipation through the surface of the housing 12 from the active elements deployed inside the assembly 10.

[0027] The transponder 10 is designed to be compliant with the OIF (Optical Internetworking Forum)—VSR4-01.0 implementation standard for optically transmitting OC-192 data and providing a parallel optics based VSR (Very Short Reach) OC-192/STM-64 interface. The transponder assembly 10 provides a bi-directional interface for multiplexing a sixteen-bit wide bus of 622 Mb/s electrical LVDS (Low-Voltage Differential Signal) signal data supplied from the pin-array connector 18 into 12 channels of optical signal data at 1.24 Gb/s for transmission as photonic signals over a twelve element optical ribbon cable and also for receiving 12 channels of optical signal data at 1.24 Gb/s and demultiplexing this data into a sixteen-bit wide bus of 622 Mb/s electrical LVDS signal data for supply to the pin-array connecter 18. The transponder assembly 10 also includes an error detection channel and a protection channel among the 12 optical channels. The pin-array connector 18 is intended to interface to an OC-192 framer on the electrical assembly to which the transponder assembly 10 is connected.

[0028] Referring now to FIG. 3, the transponder assembly 10 includes a parallel optics transmitter module 30, a parallel optics receiver module 32, a Flexible printed circuit or Flex circuit 34, a rigid circuit board 36 and connecter mounting board 38 all of which are mounted onto the bottom section 24 of the housing 12. The parallel optics transmitter module 30 provides an optical interface to a 12 fiber optic ribbon cable and includes a set of 12 VCSELs (Vertical Cavity Surface Emitting Lasers) for emitting optical signals in response to electrical signals which are directed into the 12 fibers of the ribbon cable and includes electrical circuitry for processing electrical signals received from a pluggable transmitter edge connector 40 and converting these signals into forms suitable for driving the VCSELs. The parallel optics receiver module 32 provides an optical interface to a 12 fiber optic ribbon cable and includes a set of 12 PIN diodes for responding to optical signals from the 12 fibers of the ribbon cable which are directed onto the diodes and converting these signals into electrical signals and includes electrical circuitry for processing the electrical signals into suitable forms for general use and supplying them to a pluggable receiver edge connecter 42. The transmitter module 30 includes a frame 44 on which the receptacle 26, heat sink 46 and a small circuit board 48 are mounted. The circuit board 48 extends along the bottom of the module 30 and carries the edge connecter 40 at its far end opposite the receptacle 26. The receiver module 32 is similarly constructed and includes a frame 45 on which the receptacle 28, heat sink 50 and a small circuit board 52 are mounted. The circuit board 52 extends along the bottom of the module 32 and carries the edge connecter 42 its far end opposite the receptacle 28. The Flex circuit 34 extends from the circuit board 36 to the connecter board 38 and includes a large number of signal lines which interconnect the circuit board 36 to the connector board 38. The Flex circuit 34 is comprised of a flexible material such as a Polyimide material supporting thin metal traces as signal lines that can be curled into an arcuate shapes while still preserving the integrity of its signal lines. The rigid circuit board 36 provides electrical circuitry for use in signal processing and includes a SerDes (Serializer/Deserializer) semiconductor chip 54 as well as other circuitry. The connecter mounting board 38 includes a pair of electrical connection jacks 60 and 62 mounted on its underside for interconnecting with the edge connecters 40 and 42 of the parallel optic modules 30 and 32.

[0029] Referring now to FIGS. 4 and 5, the parallel optic modules 30 and 32 are connected to the connector board 38 by the edge connectors 40 and 42 carried on their circuit boards 48 and 52 which are plugged into the connection jacks 60 and 62 mounted on the connecter board 38. It should be noted that the module 32, edge connecter 42, circuit board 52 and connection jack 62 are not shown in FIGS. 4 and 5 but are positioned directly behind the module 30, edge connecter 40, circuit board 48 and connection jack 60. However, discussion of the invention with reference the module 30, edge connecter 40, circuit board 48 and connection jack 60 as illustrated in the drawings should serve to fully explain the invention. The connector board 38 is in turn connected to the circuit board 36 by the Flex circuit 34. However, the Flex circuit 34 is curled into a multi-curved shape between the connector board 38 and circuit board 36 in order to allow the circuit board 36 to be deployed at a different level from the connector board 38. The plane defined by the position of circuit board 36 is intermediate between the planes defined by the positions of the connector board 38 and the circuit boards 48 and 52. This is of advantage since it allows the top of the circuit board 38 to define the top of the internal assembly within the housing 12 which otherwise would be defined at a higher level by the circuit board 36 thereby adding to the overall height of the module. Use of the Flex circuit 34 in interconnecting the modules 30 and 32 to the circuit board allows for a more compact assembly to be achieved which in turn provides a smaller form factor to the transponder assembly 10.

[0030] Referring now again to FIG. 4, the circuit board 36 includes the SerDes semiconductor chip 54 mounted on its top surface 64 and the pin-array connector 18 mounted on its bottom surface 66. The SerDes chip 54 and pin-array connector 18 are mounted directly across from one another on opposing surfaces of the circuit board 36. Both the SerDes chip 54 and the pin-array connector 18 are connected to the circuit board 36 by ball grid array attachments 70 and 72 on the opposite surfaces 64 and 66 of the circuit board 36.

[0031] Referring now to FIG. 6, a small section 75 of the circuit board 36 is shown in the vicinity of one of the ball grid array attachments. The circuit board has multiple layers 68 through which circuit traces may extend at multiple levels. This section 75 of the circuit board 36 includes two spaced apart attachment pads 74 on which solder may be deployed on the surface of the board 36 which are associated with the ball grid array. The pads 74 are connected by short circuit traces 76 to a metal plated vias 80 which extend entirely through the board 36 from surface to opposite surface. This construction is characteristic of ball grid arrays and allows the pads 74 to be selectively connected to circuit traces at any of the layers 68 of the board 36 by way of the traces 76 and metal plated vias 80.

[0032] Referring now to FIG. 7, the attachment pads 74, connection traces 76 and vias 80 associated with each of the ball grid array attachments are shown. It should be borne in mind that the circuit board 36 is not shown in this view and that the vias 80 extend through the circuit board 36 while the attachment pads 74 and traces 76 for each attachments 70 and 72 are resident on opposite surfaces of circuit board 36. The ball grid array attachment 70 for the SerDes chip is shown as having 256 pads in a square pattern. The ball grid array attachment 72 for the pin-array connector 150 18 is shown as having 300 pads in a rectangular pattern. The patterns formed by the attachments 70 and 72 define two overlapping areas 84 and 86 characterized by high densities of pads and associated traces and vias. Surface traces such as traces 78 may be used to connect to discrete surface mounted components.

[0033] Referring now to FIG. 8, a small section 85 of the circuit board 36 is shown in the overlapping area 84. This section 85 of the circuit board 36 includes two spaced apart pads 74 a on the surface 64 of the board 36 associated with the ball grid array attachment 70. The pads 74 a are connected by short circuit traces 76 a to a metal plated vias 80 a which extend entirely through the board 36 from one surface to its opposite surface. This section 85 of the circuit board 36 also includes two spaced apart pads 74 b (in phantom) on the surface 66 of the board 36 associated with the ball grid array attachment 72. The pads 74 b are connected by short circuit traces 76 b (in phantom) to a metal plated vias 80 b which extend entirely through the board 36 from one surface to its opposite surface. The vias 80 a and 80 b are deployed in an alternating pattern so that the vias of one array attachment are positioned in between the vias of the other array attachment. In this manner all of the vias 80 for ball grid arrays attachments 70 and 72 can be accommodated in the available space.

[0034] Referring now to FIG. 9, the overlapping area 84 is shown as including vias 80 associated with each of the ball grid array attachments 70 and 72 but only pads 74 a and traces 76 a associated with the attachment 70. The vias 80 c are connected to mutiple pads 74 a in cases where the circuit functionality allows for such interconnections. Certain vias may thereby be eliminated as redundant which allows for simpler construction. More importantly it allows circuit traces at multiple levels in the circuit board 36 to extend through the via-free pathways, such as space 86, thereby created for establishing connections within the board 36.

[0035] Referring now to FIGS. 10 and 11, a typical parallel optic (transmitter) module 30 is shown in greater detail as including the receptacle 26, metal support frame 44, lens and alignment frame 92, carrier assembly 94, and heat sink 46. It should be noted that the receiver module 32 would be similar in design and construction to the transmitter module 30 except that it would contain photoactive elements operative for receiving signals such as PIN diodes and associated circuitry as opposed to transmitter elements such as VCSELs. The receptacle 26 is mounted in the recess 98 in the support frame 44 so that it abuts the back wall 102 of the frame 44. The carrier assembly 94 includes the printed circuit board 48, the module Flex circuit 106 and the carrier frame section 108. The lens and alignment frame 92 is mounted in between the frame section 108 of the carrier assembly 94 and the back wall 102 of the support frame 44 so that it is immediately adjacent to the fiber ends on the proximal end of the connecter ferrule for the fiber optic ribbon cable when the ferrule is latched into the module 30. The Flex circuit 106 connects the frame section 108 to the circuit board 48 serving as a medium for providing a large number of connection lines between components on the carrier frame section 108 and the circuit board 48 including the microcontroller chip 110 and the edge connecter 40. The circuit board 48 fits along the back shelf 112 of the support frame 44 underneath the heat sink 46. The front end 114 of the heat sink 46 abuts the backside of the carrier frame section 108 for dissipating heat generated during operation by the electrical components mounted onto the frame section. The bolts 116 help retain the heat sink 46 and circuit board 48 in position within the frame 44. The support frame 44 includes a window 118 in its back wall 102. The lens and alignment frame 92 includes a mostly planar base 120 and a rectangular tower structure 122 projecting forward of the base 120 on which guide pins 124 and a lens array 126 are mounted. The tower structure 122 of the lens and alignment frame 92 fits through the window 118 of the support frame 44 in the assembled device. The lens and alignment frame 92 is a one-piece precision plastic injection-molded part including the tower structure 122, guide pins 124 and lens array 126. The carrier frame section 108 of the carrier assembly 94 preferably includes one or more layers of printed circuit board material including a layer of Flex circuit material which is an extended part of the Flex circuit 106. An optoelectronic device 130 containing photoactive semiconductor components is precisely mounted on the frame section 108. The device 130 comprises an integrated circuit chip which contains 12 VCSELs which are deployed on and as part of the chip. The photoactive components are disposed in a linear array at regular intervals corresponding to the lens array 126 and the array of fibers in the fiber optic ribbon cable connecter. When the lens and alignment frame 92 is mounted on the frame section 108 the optoelectronic device 130 and its photoactive components (VCSELs) are precisely aligned with the lens array 126 and the guide pins 124. One or more signal processing chips 132 may be mounted on the carrier frame section 108 for communicating with the optoelectronic device 130 and more particularly providing drive signals to transmitter elements (or providing signal amplification and conditioning in the case of receiver elements).

[0036] Although only a few embodiments of the present inventions have been described in detail, it should be understood that the present invention may be embodied in other forms without departing from the overall spirit or scope of the present invention. 

1. An optoelectronic transponder assembly, comprising: a) a receiver module for interfacing with the end connector of an fiber optic communications cable and for converting optical signals to electrical signals; b) a transmitter module for converting electrical signals to optical signals and for interfacing with the end connector of an fiber optic cable; c) a printed circuit board, including: a semiconductor chip adapted for signal processing, a first ball grid array for mounting said semiconductor chip on one surface of said board, an electrical connector adapted for connecting with a computer or communications system, and a second ball grid array overlapping with said first ball grid array for mounting said electrical connector on the other surface of said board directly across from said semiconductor chip; and d) means for electrically connecting said transmitter and receiver modules with said printed circuit board.
 2. The transponder assembly of claim 1, wherein: said electrical connector comprises a pin-array connector, and said semiconductor chip comprises a SerDes chip.
 3. The transponder assembly of claim 1, wherein: said means for electrically connecting includes a Flex circuit.
 4. The transponder assembly of claim 1, wherein: said modules are parallel optics subassemblies which are adapted for interfacing with fiber optic ribbon cables containing multiple optical fibers.
 5. The transponder assembly of claim 3, wherein said means for connecting further includes: a pair of electrical connection jacks for interconnecting with said modules and a connecter board coupled to said Flex circuit on which said jacks are mounted.
 6. A printed circuit board assembly, comprising: a) a multi-layer printed circuit board, including: i) a first ball grid array on a first surface of said board having a first set of vias, ii) a second ball grid array on a second surface of said board overlapping with said first ball grid array and having a second set of vias positioned in between said first set of vias; b) an electrical connector attached to said first ball grid array on said first surface of said board; and c) a semiconductor chip attached to said second ball grid array across from said electrical connector on said second surface of said board.
 7. The printed circuit board assembly of claim 6, in which: said electrical connector comprises a pin-array connector, and said semiconductor chip comprises a SerDes chip.
 8. The printed circuit board assembly of claim 6, further including: pathways in between the vias from both said first and second sets of vias positioned in the regions where the ball grid arrays overlap for allowing electrical traces within said circuit board to pass through said regions.
 9. The printed circuit board assembly of claim 6, further including: a Flex circuit attached to said printed circuit board for electrically interconnecting said circuit board to an optical subassembly.
 10. A printed circuit board adapted for mounting an electrical connector and a semiconductor chip so that said electrical connector is directly across from said semiconductor chip on the opposite surface of said board, said board comprising: a) a first region defined by a first ball grid array attachment having a first set of vias and associated contact pads on one surface of said board for mounting said electrical connector; b) a second region defined by a second ball grid array attachment having a second set of vias and associated contact pads on the opposite surface of said board for mounting said semiconductor chip; and c) a third region defined by an overlap between said first and second ball grid array attachments and including vias and contact pads from both said first and second sets of vias.
 11. The printed circuit board of claim 10, in which: said electrical connector comprises a pin-array connector.
 12. The printed circuit board of claim 10, in which: said third region includes one or more pathways between the vias in said third region for allowing electrical traces to pass through said third region.
 13. The printed circuit board of claim 10, further including: one or more traces on the surface of said board for interconnecting said ball grid array contact pads which share the same electrical signals whereby the number of required vias can be reduced in order to help provide for said pathways.
 14. The printed circuit board of claim 10, in which: said semiconductor chip comprises a SerDes chip. 